PHOTOSYNTHETIC CAPACITY CHANGES IN PELTIGERA .2. CONTRASTING SEASON PATTERNS OF NET PHOTOSYNTHESIS IN 2 POPULATIONS OF PELTIGERA-RUFESCENS

The seasonal net photosynthetic response matrix to moisture, temperature and light was examined in 2 populations of P. rufescens (Weis) Mudd, geographically widely separated and representative of arctic and temperate climates, respectively. The arctic population shows a seasonally constant net photosynthetic rate whereas the temperate population exhibits a marked summer increase of photosynthetic capacity under high temperatures and levels of illumination. This change in capacity is shown by use of photosynthetic-illumination curves to be due to temperature acclimation, presumably involving a seasonal enzymatic change in the Calvin cycle. Experimental induction of the summer or winter response can be achieved by storage of air-dry thalli under an appropriate combination of ambient temperature and day length. The data are discussed both in relation to the ecology of the 2 contrasting populations and to seasonal changes in the photosynthetic capacity of other lichen species.